kernel_5.10 no rt

hc

2023-12-11 6778948f9de86c3cfaf36725a7c87dcff9ba247f

 kernel/include/linux/u64_stats_sync.h
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@@ -3,33 +3,36 @@
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 #define _LINUX_U64_STATS_SYNC_H
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 /*
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- * To properly implement 64bits network statistics on 32bit and 64bit hosts,
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- * we provide a synchronization point, that is a noop on 64bit or UP kernels.
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+ * Protect against 64-bit values tearing on 32-bit architectures. This is
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+ * typically used for statistics read/update in different subsystems.
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  *
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  * Key points :
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- * 1) Use a seqcount on SMP 32bits, with low overhead.
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- * 2) Whole thing is a noop on 64bit arches or UP kernels.
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- * 3) Write side must ensure mutual exclusion or one seqcount update could
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+ *
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+ * -  Use a seqcount on 32-bit SMP, only disable preemption for 32-bit UP.
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+ * -  The whole thing is a no-op on 64-bit architectures.
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+ *
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+ * Usage constraints:
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+ *
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+ * 1) Write side must ensure mutual exclusion, or one seqcount update could
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  *    be lost, thus blocking readers forever.
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- *    If this synchronization point is not a mutex, but a spinlock or
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- *    spinlock_bh() or disable_bh() :
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- * 3.1) Write side should not sleep.
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- * 3.2) Write side should not allow preemption.
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- * 3.3) If applicable, interrupts should be disabled.
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+ *
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+ * 2) Write side must disable preemption, or a seqcount reader can preempt the
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+ *    writer and also spin forever.
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+ *
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+ * 3) Write side must use the _irqsave() variant if other writers, or a reader,
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+ *    can be invoked from an IRQ context.
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  *
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  * 4) If reader fetches several counters, there is no guarantee the whole values
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- *    are consistent (remember point 1) : this is a noop on 64bit arches anyway)
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+ *    are consistent w.r.t. each other (remember point #2: seqcounts are not
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+ *    used for 64bit architectures).
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  *
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- * 5) readers are allowed to sleep or be preempted/interrupted : They perform
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- *    pure reads. But if they have to fetch many values, it's better to not allow
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- *    preemptions/interruptions to avoid many retries.
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+ * 5) Readers are allowed to sleep or be preempted/interrupted: they perform
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+ *    pure reads.
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  *
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- * 6) If counter might be written by an interrupt, readers should block interrupts.
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- *    (On UP, there is no seqcount_t protection, a reader allowing interrupts could
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- *     read partial values)
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- *
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- * 7) For irq and softirq uses, readers can use u64_stats_fetch_begin_irq() and
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- *    u64_stats_fetch_retry_irq() helpers
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+ * 6) Readers must use both u64_stats_fetch_{begin,retry}_irq() if the stats
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+ *    might be updated from a hardirq or softirq context (remember point #1:
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+ *    seqcounts are not used for UP kernels). 32-bit UP stat readers could read
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+ *    corrupted 64-bit values otherwise.
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  *
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  * Usage :
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  *
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@@ -40,8 +43,8 @@
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  *   spin_lock_bh(...) or other synchronization to get exclusive access
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  *   ...
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  *   u64_stats_update_begin(&stats->syncp);
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- *   stats->bytes64 += len; // non atomic operation
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- *   stats->packets64++;    // non atomic operation
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+ *   u64_stats_add(&stats->bytes64, len); // non atomic operation
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+ *   u64_stats_inc(&stats->packets64);    // non atomic operation
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  *   u64_stats_update_end(&stats->syncp);
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  *
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  * While a consumer (reader) should use following template to get consistent
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@@ -52,8 +55,8 @@
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  *
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  * do {
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  *         start = u64_stats_fetch_begin(&stats->syncp);
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- *         tbytes = stats->bytes64; // non atomic operation
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- *         tpackets = stats->packets64; // non atomic operation
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+ *         tbytes = u64_stats_read(&stats->bytes64); // non atomic operation
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+ *         tpackets = u64_stats_read(&stats->packets64); // non atomic operation
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  * } while (u64_stats_fetch_retry(&stats->syncp, start));
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  *
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  *
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@@ -68,6 +71,49 @@
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 #endif
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 };
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+#if BITS_PER_LONG == 64
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+#include <asm/local64.h>
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+
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+typedef struct {
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+	local64_t	v;
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+} u64_stats_t ;
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+
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+static inline u64 u64_stats_read(const u64_stats_t *p)
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+{
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+	return local64_read(&p->v);
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+}
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+
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+static inline void u64_stats_add(u64_stats_t *p, unsigned long val)
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+{
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+	local64_add(val, &p->v);
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+}
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+
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+static inline void u64_stats_inc(u64_stats_t *p)
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+{
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+	local64_inc(&p->v);
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+}
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+
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+#else
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+
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+typedef struct {
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+	u64		v;
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+} u64_stats_t;
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+
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+static inline u64 u64_stats_read(const u64_stats_t *p)
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+{
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+	return p->v;
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+}
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+
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+static inline void u64_stats_add(u64_stats_t *p, unsigned long val)
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+{
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+	p->v += val;
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+}
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+
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+static inline void u64_stats_inc(u64_stats_t *p)
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+{
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+	p->v++;
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+}
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+#endif
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 #if BITS_PER_LONG == 32 && defined(CONFIG_SMP)
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 #define u64_stats_init(syncp)	seqcount_init(&(syncp)->seq)